The objective of this research proposal is to saturate the genome of SV40 with point mutations for the purpose of understanding the functional relationships among SV40 gene products, especially those which lead to and alter malignancy. This goal will be accomplished by selectively mutagenizing specific underrepresented regions of the chromosome by taking advantage of the mode of action of certain mutagens, the mutational blocks in existing mutants, and the relative ease of genetic manipulation of SV40. In order to increase the likelihood of identifying mutations throughout the genome, temperature-sensitive, point-lethal, and host range-transformation mutants will be isolated and characterized as to phenotype and map location. The identification of point mutations in all possible regions of the SV40 genome and characterization of the alterations they produce should add significantly to our understanding of the functioning of viral information during lytic infection and transformation.